Hello Filippo,
Thank you for contacting Apple Developer Program Support regarding issues in iTunes Connect.
I understand that you are not able to create a new app in iTunes Connect which I can understand is concerning. I am happy to investigate this issue, however I need more information to assist you. Please provide the following:
Web browser and version
Steps to reproduce the issue
Exact text of any alert messages
Screenshots illustrating the issue in the latest version of Safari
Affected devices including the model, generation, and OS version